Studies on lymphocytes from rat's milk will be continued. The capacity of these cells (a) to abolish tolerance in adult syngeneic hosts, (b) to induce tolerance when injected intravenously into neonatal allogenic hosts, (c) to incite both local and systemic GVH reactions, and (d) to act as reactants in Mixed Lymphocyte Cultures will be evaluated. Milk lymphocytes will also be labeled with appropriate radioisotopes, fed to neonatal rats and their egress from the lumen of the gut and ultimate fate studied. In other experiments, labeled lymphoid cells of various types will be transferred to syngeneic lactating hosts and their possible uptake and transfer to the milk will be evaluated. Experiments will be carried out further to analyze the basis of the augmented reproductive performance displayed by uteri specifically sensitized against alloantigens of the conceptuses. Labeled spermatozoa and lymphocytes will be introduced into the uterine lumen and their uptake and dissemination studied. Studies on the response of Syrian hamsters to weak transplantation antigens will continue to include strains other than MHA and LSH; PD4, LHC as well as the other two strains, exhibit the type of tolerance and adjuvant effect previously described. Since this work has important implications for the ability of an animal to handle tumor grafts, three different hamster tumor cell lines have been obtained from investigators at other institutions. Two of these tumors arose in the LSH strain, while the other is from an outbred source. The immunologic response of hamsters to these tumors which possess tumor-specific antigens will be manipulated in an effort to induce tolerance and/or a high degree of sensitivity by the maneuvers described for the response to weak transplantation antigens on skin grafts. As an outgrowth of immunoglobulin studies during the course of systemic graft-versus-host disease in Syrian hamsters, we have begun to investigate the cellular basis for the relatively poor antibody responses hamsters make to certain antigens. Preliminary studies indicate that while hamsters are capable of making IgG antibody to sheep RBCs, they are deficient in this regard and make the switch from IgM to IgG only with great difficulty. Because of the suspected genetic abberation at the hamster major histocompatibility locus, and because of the suspicion that the gene products encoded for by this gen (Text Truncated - Exceeds Capacity)